The ignition delay dependence on fuel ignitability and operating conditions including intake oxygen concentrations and intake gas temperatures were investigated in a DI diesel engine with a common-rail fuel injection system and cooled EGR. Increases in ignition delays when reducing the intake oxygen concentration from 21% to 15% are larger with lower ignitability fuels. The ignition delay dependence on intake oxygen concentration is weaker with higher ignitability fuels and stable operation is possible under the low intake oxygen concentrations. Increases in ignition delays when lowering intake gas temperatures is slightly larger with lower ignitability fuels. Under practical conditions with the intake oxygen concentration between 21% and 15% and the intake gas temperature between 40℃ and 100℃, the changes in ignition delays with the intake oxygen concentration are more significant than with intake gas temperature.
